Individual optical devices in optical circuits are giving way to integrated optical devices in much the same manner as their semiconductor counterparts did in the past. These optical circuits comprise waveguides, directional couplers as well as optical sources. At present, integrated optical devices comprise a substrate on which a small number of components are fabricated. The exact characteristics of an integrated optical circuit are difficult to predict because of the sensitivity of waveguide parameters to slight variations in the fabrication process. This has forced integrated optic (IO) manufacturers to accept low yields and avoid 10 circuits which contain too many (greater than 2) critical components such as directional couplers.
Recently, the Annealed Proton Exchange (APE) process has been developed for LiNbO.sub.3 and LiTaO.sub.3 integrated optic fabrication. The APE process has eased the fabrication constraints by allowing the fabricator to trim the entire circuit by annealing the device in an oven to achieve greater diffusion of the exchange ion. The known method of annealing results in an optical index of refraction profile which has a lesser gradient in the index of refraction of the waveguide (delta n), and larger device crossection with that change of refractive index. This process works quite well except that it is not possible to selectively anneal localized regions of the circuit. Furthermore, circuit annealing while monitoring its characteristics is extremely cumbersome, since it takes place in a 300.degree.-400.degree. C. oven.
Very often, the waveguide characteristics are fairly sensitive to the anneal times and the results of a short anneal may not be easily predicted. In critical applications, the devices must be benched tested and trimmed by a further annealing step. Up until now, the annealing process has been done in an oven, at temperatures between 300.degree. and 400.degree. C. and there has been no demonstration of a method which would allow the annealing of IO waveguides while monitoring their progress. A method and apparatus for selectively annealing small sections of an IO circuit device while monitoring a relevant optical circuit parameter would alleviate many if not all of these problems. Its impact on integrated optics would be analogous to active trimming of thick and thin film resistors in the electronics component and hybrid industries. The present invention is directed towards such a device.
Related subject matter can be found in the commonly owned U.S. Pat. No. 4,953,935 entitled "Integrated Optic Star Coupler", and U.S. patent applications Ser. Nos. 329,121 entitled "Single Polarization Integrated Optical Components for Optical Gyroscopes" and 329,123 entitled "Low Loss Proton Exchanged Waveguides for Active Integrated Optic Devices", all incorporated herein by reference.